1. Field of the Invention
The present invention relates to a pretensioner device which is used in a seat belt device for a vehicle. The pretensioner device is a device which, at the time of rapid deceleration of a vehicle or the like, decreases the amount of movement of the waist portion of a vehicle occupant to which a webbing for restraining a vehicle occupant is applied, by pulling-in a buckle or an anchor plate.
2. Description of the Related Art
Among seat belt devices for vehicles, there are three-point seat belt devices using a continuous webbing.
In this type of seat belt device, one end portion of the webbing is anchored to a take-up device (retractor), the intermediate portion of the webbing passes through a through-anchor fixed to the upper portion of the center pillar, and the other end portion of the webbing is anchored on an anchor plate. A tongue plate is disposed at the intermediate portion of the webbing between the anchor plate and the through-anchor. By anchoring the tongue plate in a buckle device disposed at the side of a seat, the webbing is pulled out from the retractor and applied to the vehicle occupant.
In this state, the shoulder webbing, which is from the through-anchor to the tongue plate (the buckle device), restrains the upper body of the vehicle occupant, whereas the lap webbing, which is from the tongue plate to the anchor plate, restrains the waist portion of the vehicle occupant. Among such seat belt devices, there are those which are provided with a lap pretensioner device for tensing, in the direction of restraining the vehicle occupant, the webbing at the time of a rapid deceleration of the vehicle, such as at the time of a collision or the like.
This type of lap pretensioner device is formed to include a piston, a cylinder, and a base cartridge. The piston is formed to be cylindrical, and is connected to a buckle via a wire which serves as a connecting member. The piston is disposed at one end side of the cylinder and is accommodated in the cylinder. The piston is movable toward the other end side of the cylinder. The intermediate portion of the wire is connected to the one end side of the cylinder and is bent back toward the cylinder. The base cartridge is a member through which the bent-back intermediate portion of the wire is inserted.
A guiding portion (entrance portion) and a gas chamber are formed so as to communicate with one another at the interior of the base cartridge through which the intermediate portion of the wire is inserted. The guiding portion is a portion through which the bent-back wire is inserted so as to be slidable in a linear direction which is coaxial with the cylinder. The gas chamber is provided between the guiding portion and the cylinder, and has a diameter which is substantially larger than that of the guiding portion. A gas generator, which is mounted to the base cartridge, communicates with the gas chamber so as to be able to supply gas thereto. The gas generator is an example of a gas generating device which, by being operated, ignites a gas generating agent so as to generate a large amount of gas.
The gas generator is operated when an acceleration sensor detects a predetermined acceleration. The piston is moved within the cylinder in the axial direction toward the other end thereof due to the pressure of the large amount of gas supplied into the cylinder. The buckle is thereby pulled-in toward the vehicle body. In order to prevent flames from leaking from the base cartridge due to the gas flowing out toward the guiding portion, packing formed from rubber is disposed between the guiding portion and the gas chamber. The wire is slidably inserted through the rubber packing.
A lap pretensioner device such as that described above presupposes a case in which a stretch-out load is applied to the webbing by the inertial movement of the vehicle occupant, before operation of the gas generator. For example, there are cases in which, at the time of a rapid deceleration of the vehicle such as a collision, the detecting of the acceleration by the acceleration sensor (i.e., the operation of the acceleration sensor) is delayed.
In a conventional lap pretensioner device, if the gas generator operates after the stretch-out load is applied to the webbing, the piston, which is connected to the webbing via the buckle and the wire, cannot move toward the other end of the cylinder. As a result, there is the concern that the high-temperature gas or flames which cannot move properly from the gas chamber may leak to the exterior from the guiding portion side through the sealed portion formed by the packing.
In order to prevent such a phenomenon from occurring, there is the need for special measures such as, for example, mounting a protective cover or the like. Such special measures lead to an increase in the cost of the lap pretensioner device. In addition, such special measures are a cause of deterioration of the mountability of the lap pretensioner device to a vehicle.